Most reported studies of the effect of splenectomy in experimental animals have shown that the lack of a spleen enhances infection. Current clinical interest involves patients of all ages who have had a splenectomy. A rapidly fatal sepsis, often Pneumococcal, can develop even years after the procedure. Although many of the patients reported have had a therapeutic splenectomy for hematologic disorders, some have developed this syndrome after a previous operation for traumatic injury to the spleen. The syndrome has probably not become well recognized because the numbers of patients, although statistically significant, are small. Most previous experimental methods for demonstrating susceptibility to infection have involved intravenous or intraperitoneal injection of bacteria. The method assures accurate dosage, but many may not mimic the natural history of the disease. The proposed research project involves the aerosol inhalation of uniform numbers of Pneumococci in a commercial exposure chamber (Tri-R). Normal, sham-operated, and splenectomized animals will be exposed to uniform group concentrations of bacteria and differences observed in: 1) death rates; 2) observed illness rates followed by recovery; and 3) extent of pneumonia. Anticipating an increased susceptibility to inhaled Pneumococci, we propose to study in the splenectomized animals: 1) role of penicillin prophylaxis; 2) partial rather than total splenectomy; 3) splenic artery ligation with the spleen remaining in situ; and 4) splenic autotransplantation (splenosis).